The invention relates to a sprayer boom on a vehicle and of the kind which has a number of liquid nozzles for spraying the carriageway during driving with a liquid fed under pressure to the nozzles from a storage container via a feed pipe.
For economic and environmental reasons, it is usually advantageous not to use more spray liquid per area unit than what is highly necessary. This applies to e.g. spraying crops with pesticides or icy and snow-slippery roads with a brine.
During spraying, the vehicle must often change speed. Thus, a salt truck spraying brine on icy roads in a town has, to a great or small extent, to follow the changing rhythm of the traffic.
The quantity of brine which is necessary to spray the carriageway with per area unit should however always be the same irrespective of the speed. Neither more nor less. The salt trucks are therefore often provided with equipment for regulating the liquid flow to the nozzles in proportion to the speed.
The hydrodynamic laws of flowing liquids mean that a given nozzle can only function optimally within a relatively narrow flow regime.
Normally, modem salt trucks are therefore provided with several sets of nozzles, each set for each their flow regime. In this case, the sprayer boom is fitted with a row of revolvable nozzle holders, each carrying a number of nozzles set to each their specific flow.
The operator can now revolve the set of nozzles that matches the flow best at a given speed into the operational position so that the salting is done with optimally functioning nozzles.
When the speed changes, the operator then revolves another set of nozzles into operational position. In order to be able to do this, he must however get out of the cab, crawl in under the boom and manually revolve nozzle head after nozzle head until all nozzles in the next nozzle set are put in position.
The work of changing nozzles in this way is extremely difficult and time-consuming and especially so when it has to be done with short intervals. It is hardly possible to change the nozzles frequently enough in heavy traffic. Furthermore, the operation must often be done under extremely unpleasant working conditions where the operator has to crawl around on a cold, dirty and wet road in an uncomfortable position under the boom.
The example with the salt truck shows the way the problem presents itself at spraying tasks that take place with variable speed across an area.
For spraying of crops with e.g. pesticides from a sprayer boom on a tractor, it is for the sake of the environment advantageous to spray liquid quantity at the accepted minimum quantity per area unit whether the tractor is going slowly or fast.
For spraying with liquid fertilizers, it can moreover be necessary to proportion the extent of the fertilization to the character of the soil and the crops which are grown in the soil.
The object of the invention is to provide a sprayer boom of the kind mentioned in the opening paragraph with nozzle sets which can be put in optimum function at a given liquid flow more quickly and easily than known so far.
A novel and unique feature according to the invention, whereby this is achieved, is the nozzles are divided into sets, each with their valve arrangement for selectively shutting off and opening for liquid supply to the respective set. The nozzles which match a given situation can therefore be put in operation quickly and easily without the operator having to get out of the cab. The process can take place automatically without active contribution from the operator when each valve arrangement is arranged to open at a liquid flow volume through the feed pipe, which is fixed individually for the respective valve arrangement.
In an expedient embodiment, the nozzles sets can be placed one set each on their nozzle pipe, wherein the nozzle pipes two by two are liquidly interconnected to a cross pipe, in which is built-in a partition with a pressure valve for opening a passage through the respective partition at a prefixed liquid pressure.
In this case, only one of the nozzle pipes is directly fed with liquid from the feed pipe while the valves of the rest of the nozzles pipes are automatically opened like a cascade as the flow rises.
In a variant of this embodiment, the sprayer boom can have a manifold connected to the feed pipe and having a number of projecting nozzle pipes with a number of chambers defined by partitions with each their pressure valve for opening a passage through the respective partition at a prefixed liquid pressure, a nozzle being placed at each chamber. This construction is very reliable as admission of liquid to one or more nozzle sets do not depend on whether one single valve might fail.
When the nozzle sets are placed on each their nozzle pipes which, via each their liquid pipe with an inserted valve, is connected to a manifold which again is connected to the feed pipe, a nozzle pipe can optionally be connected from the cab by e.g. a rod system for activating the valves. In this case, the operator can read a speedometer and a flowmeter in the cab and, on the basis of his observations, calculate the combination of nozzle pipes which would be the optimum in a given situation. The solution is inexpensive and simple and can advantageously be employed when the nozzle sets only have to be changed at relatively long intervals.
In case of frequent changes, it would be better to employ an electronic control system with detectors for continuously registering liquid flow and speed respectively and transmitting the registered values as signals to a computer which, on the basis of the received signals, calculates the immediate optimum valve position and signals the valves to regulate themselves into these positions.
An especially simple and inexpensive control system can be obtained with a detector which registers e.g. the rotational speed of a wheel and converts this to control signals in the form of an impulse current or a voltage, which is a function of the registered speed.